A conventional air-conditioning system for a vehicle is disclosed, for example, in Japanese Patent Publication No. H10-53019, which has a heat accumulator for storing heat of refrigerant (heat of cooling) in addition to an evaporator to which refrigerant compressed by a compressor is supplied. The compressor is driven by an internal combustion engine mounted on a vehicle. According to the conventional system, cooling operation can be continuously performed by use of the heat stored in the heat accumulator even during a period in which the engine operation is temporally stopped.
Another conventional air-conditioning system is disclosed, for example, in Japanese Patent Publication No. 2003-120544, in which the air-conditioning system has an electric motor as a driving source for the compressor, in addition to the internal combustion engine. When the engine operation is temporally stopped, as a function of an idling stop, the compressor is driven by the electric motor, so that the cooling operation for a vehicle inside is continuously carried out even during the period of the idling stop.
Although each of the above conventional air-conditioning systems has a function of continuing the cooling operation during the engine operation is stopped, cost increase is not avoidable because an additional component is necessary. In particular, frequency for such function (the continuous cooling operation during the engine stop) is not so high. Therefore, the advantage of the additional function becomes relatively smaller for the increase of cost for the additional component.
The above problem (relatively smaller effect for a large number of components) commonly exists not only in the above air-conditioning systems but also in a vehicle air-conditioning system having multiple thermal sources (for heat of cooling) or in a vehicle air-conditioning system having a compressor operated by multiple driving sources.